Regions have been identified in certain oxyuroid nematodes which stain vitally with quinone-imine dyes. Thelastoma attenuatum shows colour in the arcade cells, the small pseudocoelomocytes and the giant pseudocoelomocytes; while Leidynema appendiculata and Hammerschmidtiella diesingi possess only giant pseudocoelomocytes. All these regions have been studied.

The giant pseudocoelomocytes in all three species are apparently very active, but their precise function had not yet been assessed.

The structure of the arcade cells and small pseudocoelomocytes of Thelastoma have been described. These regions may also be active but their function is again not understood.

Further work to elucidate these problems is suggested.

Mice infected with as few as ten eggs of the nematode Trichuris muris are highly resistant to a challenge infection given 5 weeks later. The rate of elimination of challenge larvae is similar in mice immunized by infection with ten or with 300 eggs. Stimulation of immunity to challenge by the low-level infections is dependent upon the persistence of the immunizing worm population and removal of the population at day 14 considerably reduces the level of immunity. Worms developing from a low-level immunizing infection are not eliminated by a ‘self-cure’ response, as is the case with larger infections, and become sexually mature. Adult worms from such an infection are, however, eliminated by the response to a superimposed challenge infection. Repeated infection of mice with small numbers of eggs stimulates an immune response and the worm population is eliminated before patency.

The efficiency of assimilation of carbon and nitrogen by Littorina saxatilis, as calculated from the carbon and nitrogen content of food and faeces, showed that the efficiency of snails infected with rediae of Cryptocotyle lingua did not differ significantly from that in non-infected snails.

Similarly, the rate of ingestion and the rate of assimilation of infected snails did not differ significantly from those of non-infected snails.

It is suggested that this harmonious relationship reflects the longterm strategy of Cryptocotyle lingua infections.

The structure of H. placei adult worms, obtained from calves at 4, 7, 10 or 11–13 weeks after primary infection, has been studied. A reorganization of rough endoplasmic reticuhim in the cytoplasm of the gut cells was seen at 10 weeks and this was followed by marked vacuolation of many of these cells, associated with an increase in lipid production. Increases of lipid were also found in the hypodermis, lateral cords and occasionally muscle cells of worms examined at 11–13 weeks after infection.

It is suggested that these changes are the result of the host immune response, because they resemble changes which occur in the rat nematode Nippostrongylus brasiliensis and which are known to be caused by host immunity.

The junction between the gregarine trophozoite Nematocystis magna Schmidt and an epithelial cell of its earthworm host Lumbricus terrestris Muller consists of an extensive folding and meshing of the single trilaminar membrane bounding the host cell and the complex folded multilaminar limiting membrane of the trophozoite. They are separated by a structureless intercellular region of some 50 nm in width. Specialized communicating regions or permeable elements were not observed. Transport of a radioactive label across non-junctional and junctional membranes was demonstrated by using tritiated glucose. The attachment organelle of the trophozoite is shown to be capable of allowing metabolites to pass into the cell directly from the host tissue.

Trypanosoma bouffardi Leger & Blanchard, 1911, is described from naturally infected Lagonosticta s. senegala, Estrilda b. bengalus, Vidua chalybeata, Estrilda t. troglodytes and Amadina f. fasciata, all of which are new host records for Nigeria; Vidua chalybeata is a new host record for trypanosomes.

There was no significant morphological difference between populations of this trypanosome in the various natural and experimental vertebrate hosts.

T. bouffardi was transmissible to nine species of Ploceidae belonging to the three subfamilies Estrilinae, Ploceinae and Viduinae; but not to Pycnonotus barbatus, chickens or pigeons.

The parasitaemia produced by infections of T. bouffardi reached 4·1 × 105 parasites/mm3 of blood.

Reproduction of the trypanosomes was synchronous and discontinuous and occurred in the blood by unequal binary fission of trypomastigotes. Occasionally longitudinal equal binary fission of trypomastigotes also took place. There was no concentration of dividing forms in the tissues.

T. bouffardi did not grow on NNN medium although it has been grown for a short time on the medium described by Yesufu (1970).